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Title: Mesoscopic superconductivity in ultrasmall metallic grains

A nano-scale metallic grain (nanoparticle) with irregular boundaries in which the single-particle dynamics are chaotic is a zero-dimensional system described by the so-called universal Hamiltonian in the limit of a large number of electrons. The interaction part of this Hamiltonian includes a superconducting pairing term and a ferromagnetic exchange term. Spin-orbit scattering breaks spin symmetry and suppresses the exchange interaction term. Of particular interest is the fluctuation-dominated regime, typical of the smallest grains in the experiments, in which the bulk pairing gap is comparable to or smaller than the single-particle mean-level spacing, and the Bardeen-Cooper-Schrieffer (BCS) mean-field theory of superconductivity is no longer valid. Here we study the crossover between the BCS and fluctuation-dominated regimes in two limits. In the absence of spin-orbit scattering, the pairing and exchange interaction terms compete with each other. We describe the signatures of this competition in thermodynamic observables, the heat capacity and spin susceptibility. In the presence of strong spin-orbit scattering, the exchange interaction term can be ignored. We discuss how the magnetic-field response of discrete energy levels in such a nanoparticle is affected by pairing correlations. We identify signatures of pairing correlations in this response, which are detectable even in the fluctuation-dominated regime.
Authors:
 [1] ;  [1] ;  [2]
  1. Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, CT 06520 (United States)
  2. (France)
Publication Date:
OSTI Identifier:
22307988
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1619; Journal Issue: 1; Conference: 4. conference on nuclei and mesoscopic physics 2014, East Lansing, MI (United States), 5-9 May 2014; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BCS THEORY; CHAOS THEORY; COMPARATIVE EVALUATIONS; CORRELATIONS; ELECTRONS; ENERGY LEVELS; EXCHANGE INTERACTIONS; FLUCTUATIONS; HAMILTONIANS; MAGNETIC FIELDS; MEAN-FIELD THEORY; NANOPARTICLES; ORBITS; SCATTERING; SPECIFIC HEAT; SPIN; SUPERCONDUCTIVITY